Measurement Techniques, Vol. 45, No. 10, 2002

A COMPUTERIZED DYNAMOMETER TESTING WORKSTATION

S. G. Sinichkin, E. A. Kostyunin, V. G. Chervyakova, and K. K. Savrovskii

UDC 531.781

Design experience is presented for a computerized workstation for checking dynamometers, which is based on an OD-2-50 second-rank force-measuring machine, a microprocessor set of modules, and a personal computer. The procedures have been computerized for loading the dynamometers and processing the measurements, in which all the resulting documents are output to a printer. Key words: force-measuring machine, computerized workstation, sensor unit, software.

The Nizhnii Novgorod Center for Standardization, Metrology, and Certification checks dynamometers and force sensors with an OD-2-50 second-rank force-measuring machine. The original control system for the machine was developed in the early 1990s by the principal expert at the center, A. V. Priporov, and it provided automatic load setting by means of coded-contact sensors providing set loads, which could be set with decade switches. The control unit employed K155 microcircuits. Its main deficiencies were due to the poor reliability of the sensors, the lack of interlocks on the asynchronous drive motors in the loading system, and manual data processing. There are many different types of dynamometers and force sensors, while checking them is laborious because it is necessary to perform calculations, corrections, and allowance for various factors, so it has become necessary to computerize these processes. The center has collaborated with the engineering center at Nizhnii Novgorod State Technical University in developing a computerized workstation for checking dynamometers (the ARM-PD), which provides the following: • various modes of operation (manual, basic, or fully automatic); • storing data and formulas for correcting and processing results for all types of dynamometer; • storing the dynamometer checking program; • automatic processing for all the information on the procedure; • automatic overall conclusion generation; • automatic output (printout) of final documents (records, certificates, and notices); and • control system diagnosis. Figure 1 shows the block diagram of the ARM-PD; the hardware consists of two parts: units installed directly on the machine (drive motors, power supply, sensor unit, and independent control panel) and a personal computer with keyboard and printer. The independent control panel and the personal computer are linked together by an RS-232C interface. The independent control panel is based on an MCU4 microprocessor module set, with the modules standardized in size, mounting, sockets, and signals, so they can readily be linked together. Each module is connected to power supplies and 16 interface lines, which are used as a combination of a parallel interface and/or several serial ones (including user interfaces).

Translated from Izmeritel’naya Tekhnika, No. 10, pp. 69–71, October, 2002. Original article submitted May 8, 2002.

0543-1972/02/4510-1099$27.00 ©2002 Plenum Publishing Corporation

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OD-2-50 force measuring machine Test dynamometer

Drive motors

Three-phase line Power supply

ARM-PD software

RS-232C

Independent control panel

Personal computer

Printer

Keyboard

Sensor unit

Fig. 1. ARM-PD block diagram.

PC communication channel (RS-232C)

From sensors

Input module

Computing module

Output module

To power unit

Digital display

Keyboard

Power supply

Fig. 2. Block diagram of independent control panel.

The software for the independent control panel is written into the computing module in Fractal-BASIC through the RS-232C standard port in the personal computer. The BASIC interpreter is built into that module, so it is not necessary to install additional software. Figure 2 shows the block diagram of that panel. To check the execution of the controls, there are the sensor units as follows: setting loads, clamping machine, balancing, and emergency handling. There are three groups of load setting sensor appropriate to the nominal loads of 0.5, 2, and 5 tf; the load platforms for the nominal values of 0.5 and 2 tf consist of ten loads, while there are five for the 5 tf one. A line of VKB 8M inductive sensors checks the installed load, with the number of them determined by the number of nominal loads in a group (Fig. 3), i.e., the linear arrays contain ten sensors each for the 0.5 and 2 tf loads, or five for the 5 tf group. The sensors in a line interact with a steel plate, which is fixed to the mobile top of the lead screw that displaces the given group of loads. The line of sensors is located on the immobile vertical frame. The VKB 8M sensors are held in a longitudinal slot in the panel by two nuts. The body of a sensor bears a M8 thread. The slot enables one to install and regulate the sensors in accordance with the required load position. The panel with the sensors is attached by rods to the machine frame, while the rods also bear a mounting board, to which the leads from each sensor are soldered. When the measurement rate is displaced relative to the sensors, their outputs produce the unit signals D1, D2, and D3 (Fig. 3). Here, the sensors D4 and D5 produce zero signals. Then the number of installed loads is defined by the 1100

Fig. 3. Simplified force sensor design: 1) panel for mounting sensors; 2) sensors; 3) board; 4) tie; 5) base; 6) load displacement screw; 7) stand; 8) mounting board.

number of unit signals from the sensors. In other words, all the sensors together produce a combination of ones and zeros as signals, which form a code. The number of ones in the code corresponds to the number of loads used from the given group. The code produced by the sensors passes to the independent control panel for interpretation. As that coding system has redundancy, it provides improved reliability in defining the installed loads. Also, there is a software check on the sensor operation, as there is a clear-cut sequence in the generation of their unit signals. Visual monitoring can be applied to the sensors, particularly during installation and adjustment, because each includes a light-emitting diode, which lights up for each unit signal. Also, the software monitors the time needed to displace the plate from one sensor to another (from the times between the unit signals from adjacent sensors). The sensors for nominal loads of 0.5 and 2 tf work similarly. The power unit provides direct control of the drive motors, all of which are reversible, so the power unit contains five pairs of starter relays (the same as the number of motors) fitted with mechanical and electrical interlocks to prevent simultaneous operation. The motors are protected by automatic trips. All these electrical units are mounted in a plastic body with a removable lid, which provides access for servicing and repair. The ARM-PD software has two parts: for the control panel computer module and for the personal computer. The software for the personal computer is basic. The algorithms are based on methods of checking dynamometers and experience acquired in the laboratory of vibroacoustic measurements and tests at the center. Provision is made for checking third-rank and general-purpose dynamometers, including ones of DPU type, as well as force sensors. The ARM-PD has three main modes of operation: manual, basic, and fully automatic. The first allows the operator to use the independent control panel to manage the system (on-off), particularly the effector parts (clamp, load drives, and loading). In the second mode, the equipment performs a single cycle of setting a given load (from the load table) and loading the dynamometer. The fully automatic mode is the main one and enables the equipment to operate without the participation of the operator to supply a given load in percentage of the upper measurement limit for the dynamometer in accordance with one of the selected modes of loading: 1 – (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100)%; 2 – (0, 10, 20, 40, 60, 80, 100)%; 3 – (0, 10, 25, 50, 75, 100)%; 4 – (0, 20, 40, 60, 80, 100)%; 5 – nonstandard. In the last case, the operator can specify independently any points for checking. The readings at each test point are input by the operator to the computer through the keyboard, and when the measurements end, they can be corrected if necessary (temperature correction with correction coeffi1101

cients). A temperature correction is used with third-rank dynamometers if the temperature falls outside the range 20 ± 3°C. Correction by means of correction coefficients raises the accuracy and makes the machine suitable for checking force sensors of accuracy class 0.1. When the measurements have been made and corrected, the data are processed automatically and the final documents are generated: checking protocol, checking certificate or message on unsuitability, which are output to the printer. The ARM-PD in automatic mode performs the following procedures: preparation for checking; data input; measurement (modes: compression, 1–4, and nonstandard); measurement correction; measurement processing; printing the final documents; and service functions. In service-function mode, the operator can select and carry through any of the above procedures, and can also check out the machine itself and track any changes in dynamometer reading during the checks. The ARM-PD software for the above modes consists of a database and a working program. The database contains the information on the checking procedure, formulas for correcting the measurements, and reference material. The software allows the operator to interrupt the checking at any stage and to edit the database, correct the measurements, or initiate the entire checking procedure from the start or the same for individual components. When the information is printed out as a record, certificate, or message, there is provision for the operator making any necessary changes in the formulation in order to incorporate nonstandard situations. On the whole, the necessary formulation for those output documents is derived automatically from the database. The introduction of this ARM-PD equipment into the work of the center on the basis of an OD-2-50 second-rank force-measuring machine makes a considerable contribution to raising productivity and performance in checking dynamometers, while making it less laborious. The checker is completely freed from performing any calculations or filling out the final documents. The ARM-PD also has scope for extending its functions. In particular, it can be used with any OD-2-50 second-rank force-measuring machine such as is available in many branches of the State Metrological Service, including this center.

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